Fishback's choice not to double-vote Joe will go down in Survivor history as one of the all-time dumbest moves around.
Two votes for Joe wouldn't have mattered. The split made it 4 for Stephen, 3 for Abi, and 2 for Joe. So putting two on Joe would just make it 4-3-2 with 3 on Joe instead. There were two mistakes, and neither is on par with the dumbest ever. The first was splitting the votes, but that's understandable with two idols played already. The bigger one was trusting Spencer. If Spencer had voted for Joe, it would have been 3-3-3. Joe would have gone home on the re-vote.
The move was too cute and the result of over thinking, but I wouldn't call it super dumb.